Frequency mixers may be employed in a variety of electronic systems. For example, frequency mixers may be employed in radio systems to down convert a received radio frequency (RF) signal by combing the received radio frequency (RF) signal with a local oscillator (LO) signal. The combination of an input signal and an LO signal in a frequency mixer may yield an intermediate frequency (IF) signal having a frequency that corresponds to the difference between the frequencies of the input and LO signals.
In addition, the combination of an input signal and an LO signal in a frequency mixer may yield a sum signal having a frequency that corresponds to the sum of the frequencies of the input and LO signals. The sum signal may be ignored as an unwanted byproduct of a frequency mixer that is designed to yield an IF signal. Unfortunately, the sum signal may reflect back and re-enter into a mixing device and cause a degradation the performance of a frequency mixer.
Prior frequency mixers may include filter circuits that are designed to steer the sum signal to a load resistor that dissipates the energy of the sum signal. For example, a prior frequency mixer may include a diplex filter or a triplex filter coupled to the output port of the mixer. Unfortunately, a diplex filter may not have sufficient bandwidth to capture a sum signal, particularly in the case of a double balanced mixer. A triplex filter may be used in a single balanced mixer but the design of a triplex filter may be relatively complex, may require additional components, and compromise the performance of a frequency mixer.